Cross Helicity of the November 2018 Magnetic Cloud Observed by the Parker Solar Probe

Abstract

Magnetic clouds are large-scale transient structures in the solar wind with low plasma $\beta$, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter, we analyze the normalized cross helicity, ${\sigma }_c$, and residual energy, ${\sigma }_r$, of plasma fluctuations in the November 2018 magnetic cloud observed at 0.25 au by the Parker Solar Probe. A low value of $|{\sigma }_c|$ was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvénic fluctuations with high $|{\sigma }_c|$ values and ${\sigma }_r\sim 0$. These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low $|{\sigma }_c|$ is likely a common feature of magnetic clouds given their typically closed field structure. Anti-sunward fluctuations propagating immediately upstream of the cloud had strongly negative ${\sigma }_r$ values.

9 pages, 4 figures; accepted for publication in the Astrophysical Journal Letters 2020 August 17

References in corpus (11)

• The Evolution and Role of Solar Wind Turbulence in the Inner Heliosphere
• First in-situ Measurements of Electron Density and Temperature from Quasi-Thermal Noise Spectroscopy with Parker Solar Probe/FIELDS
• In-situ switchback formation in the expanding solar wind
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• Self-Similarity of ICME Flux Ropes: Observations by Radially Aligned Spacecraft in the Inner Heliosphere
• Identification of Magnetic Flux Ropes from Parker Solar Probe Observations during the First Encounter
• Cross Helicity Reversals In Magnetic Switchbacks
• Heliospheric Evolution of Magnetic Clouds
• Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath
• Implementing turbulence transport in the CRONOS framework and application to the propagation of CMEs
• Modeling the Early Evolution of a Slow Coronal Mass Ejection Imaged by the Parker Solar Probe

Cited by in corpus (4)

• Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum
• Turbulence/wave transmission at an ICME-driven shock observed by Solar Orbiter and Wind
• Multi point analysis of coronal mass ejection flux ropes using combined data from Solar Orbiter, BepiColombo and Wind
• Structure and fluctuations of a slow ICME sheath observed at 0.5 au by the Parker Solar Probe